Siobhán Cleary is also well known as a film composer having written several film scores including two feature films, Spacejacked! and Dangerous Curves directed by Jeremiah Cullinane and produced by Roger Corman. Documentary scores include Book Smugglers produced by Planet Korda Pictures and If Not You by Olga Černovaitė She also composed the score for the Andrew Legge short film, The Time-Traveller
In 1996 she was composer in residence in Bologna with the Argo Ensemble. She also worked with the Ciniteca di Bologna writing music scores to restored films, most notably the Dali/Buñuel classic Un Chien Andalou
She has attended composition courses in Italy, France and Poland where her tutors included Franco Donatoni and Louis Andriessen. She has also studied privately with Tom Johnson and Kevin Volans. She has studied film scoring with Ennio Morriocone (A Fistful of Dollars The Good, the Bad and the Ugly, The Mission) and Don Brandon Ray (Hawaii Five-O, Twilight Zone, Rawhide). In January 2006 she participated as a composer on the Moonstone Film Directors Module.